**14. Footnotes**

†Crystal data for 1,2-TFIB: C6F4I2, *M* = 401.86, brown block, 0.43 0.32 0.20 mm3, monoclinic, space group *P*21/*n* (No. 14), *a* = 10.606(4), *b* = 5.770(2), *c* = 14.548(5) Å, = 110.344(4)°, *V* = 834.7(5) Å3, *Z* = 4, *D*c = 3.198 g/cm3, *F*000 = 712, Bruker SMART APEX II CCD, MoK radiation, = 0.71073 Å, *T* = 100(2)K, 2max = 70.0º, 18326 reflections collected, 3673 unique (Rint = 0.0353). Final *GooF* = 1.105, *R1* = 0.0184, *wR2* = 0.0375, *R* indices based on 3154 reflections with I >2sigma(I) (refinement on *F*2), 109 parameters, 0 restraints. Lp and absorption corrections applied, = 7.540 mm-1. The crystal was obtained in methanol by slow evaporation. CCDC-875313 contain the supplementary crystallographic data for this structure. It can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data\_request/cif.

‡ Crystal data for co-crystals of 1,2-diiodoimidazole and 1,3,4.-diidoimidazole: C9H5I7N6, *M* = 1085.49, colourless plate, 0.19 0.15 0.08 mm3, monoclinic, space group *P*21/*m* (No. 11), *a* = 4.27080(10), *b* = 27.9241(6), *c* = 8.8926(2) Å, = 101.6110(10)°, *V* = 1038.81(4) Å3, *Z* = 2, *D*c = 3.470 g/cm3, *F*000 = 944, Bruker SMART APEX II CCD, MoK radiation, = 0.71073 Å, *T* = 100(2)K, 2max = 71.2º, 17788 reflections collected, 4803 unique (Rint = 0.0353). Final *GooF* = 1.124, *R1* = 0.0433, *wR2* = 0.0785, *R* indices based on 3855 reflections with I >2sigma(I). (refinement on *F*2), 103 parameters, 0 restraints. Lp and absorption corrections applied, = 10.461 mm-1. The crystal was obtained in methanol by slow evaporation. CCDC-875314 contain the supplementary crystallographic data for this structure. It can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data\_request/cif.

## **15. References**

162 Recent Advances in Crystallography

**13. Future perspectives** 

engineers.

**Author details** 

**Acknowledgement** 

**14. Footnotes** 

Xin Ding, Matti Tuikka and Matti Haukka

Medical Sciences grant 9P41GM103311).

MoK radiation, = 0.71073 Å, *T* = 100(2)K, 2

In Fig. 22 there is an example of a network consisting of PtCl2(NC5H4Br)2 linked together via halogen bonds. In addition to the halogen bonds, the two dimensional layers consist of weak hydrogen bonds and π-π stacking interactions. The structure shown is a good example of a

Even if the very essence of crystal engineering is to produce functional materials, a large number of studies and papers in this field are still devoted solely to the structural aspects of the molecular assemblies and frameworks. The same is true with halogen bonding. The latter is understandable since establishing the whole concept of halogen bonding has required (and still requires) a considerable amount of work. Nevertheless, examples already exist of the utilization of halogen bonding in the production of functional materials. The role of halogen bonding has been investigated in the context of the inhibition of the human protein kinase CK2α.[74]It has also been used for selective recognition of halide anions and employed in host-guest systems.[23] There are examples of the use of halogen bonding for controlling the luminescent properties of Au2-Ag2 clusters and the birefringence properties of chains of square planar Au complexes[45,75]. There are also examples of the utilization of halogen bonding in catalysis.[76] In the future the number of these types of applications is expected to grow rapidly. All of this means that halogen bonding is in the process of being transformed from a strange solid-state phenomenon to a versatile tool in the hands of crystal

*Department of Chemistry, University of Eastern Finland, Joensuu Campus, Joensuu, Finland* 

Financial support provided by the Academy of Finland (project no.139571) is gratefully acknowledged. Molecular graphics was created with the UCSF Chimera package. Chimera is developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, with support from the National Institutes of Health (National Center for Research Resources grant 2P41RR001081, National Institute of General

†Crystal data for 1,2-TFIB: C6F4I2, *M* = 401.86, brown block, 0.43 0.32 0.20 mm3, monoclinic, space group *P*21/*n* (No. 14), *a* = 10.606(4), *b* = 5.770(2), *c* = 14.548(5) Å,

110.344(4)°, *V* = 834.7(5) Å3, *Z* = 4, *D*c = 3.198 g/cm3, *F*000 = 712, Bruker SMART APEX II CCD,

unique (Rint = 0.0353). Final *GooF* = 1.105, *R1* = 0.0184, *wR2* = 0.0375, *R* indices based on 3154

=

max = 70.0º, 18326 reflections collected, 3673

network structure of a metal complex formed by halogen bonding.[70]


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